docs: def __add(self, val):
  
          """
          Helper method for range addition. It is allowed to add only one compact subrange or ``range_t`` object at once.
  
          Parameters
          ----------
          val : int or tuple or list or range
              Integer or range to add.
  
          Returns
          -------
          __has : set
              ``self.__has`` extended by `val`.
          """
  
          if not isinstance(val, range_t):
              #sanitize it
              val = {self.__val_convert(val)} # convert to a set, coz I like it that way.
  
          else:
              val = val.toset()
  
          __has = deepcopy(self.__has) # simply add to a set.
          __has.update(val)
  
          return __has